(1) Field of the Invention
The present invention relates to the field of smelting and particularly to the extraction of molten metal from a shaft furnace. More specifically, this invention is directed to improvements in apparatus for opening the tapholes which are provided at the base of the wall of a smelting furnace. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
(2) Description of the Prior Art
The molten metal produced during a smelting process in a shaft furnace is extracted from the furnace through tapholes which are provided at the base of the furnace wall. In the prior art these tapholes have, as necessary, been opened by means of a drilling process and plugged by means of the injection therein of a material which solidifies to define a very hard resistant stopper in the taphole. The plugging is performed by apparatus known in the art as "clay guns" and it is the hardened "clay" which has been removed, to open the taphole, with a percussive drill. These drilling and plugging operations are typically repeated several times a day and, in the case of large capacity furnaces, at several points about the furnace. For further information with regard to prior art "clay guns" and taphole driling devices, reference may be had to U.S. Pat. Nos. 3,765,663; 4,058,300; 4,063,772; 4,097,033; 4,195,825; 4,201,373 and 4,227,682, all of which are assigned to the assignee of the present invention.
A recent innovation in the plugging and drilling of furnace tapholes comprises the insertion of a metal drill rod in the plugging material whereby, upon hardening of the plugging material, the rod will form an integral part of the taphole stopper. The rod, which passes through the plugging material from the exterior of the furnace to the interior, is left in position. When the taphole has to be reopened, the metal drill rod is engaged by a percussion type instrument which loosens the rod and permits its extraction. This technique of opening a shaft furnace taphole has a number of advantages. Firstly, the drill rod may be reused and, by way of contrast with the drill bits previously employed to drill out the plugging material, the drill rod need not be fabricated from an expensive special steel. Additionally, the withdrawal of a metal drill rod which has been left in place in the taphole plug results in the formation of an opening which has a greater length to diameter ratio than those formed by the prior drilling processes. This is considered a significant advantage since the small diameter opening is more suitable for high pressure furnaces and prolongs the period during which the molten metal is withdrawn from the furnace thereby facilitating the handling of this molten metal.
In order to extract a drill rod from hardened plugging material, it is possible to employ conventional percussive type drilling devices provided that they are capable of producing both longitudinal vibratory motion in both directions. However, the prior art drills must be provided with a device which will engage, preferably automatically, the drill rod so that the motion generated by the tool may be imparted thereto. If the coupling of the percussive instrument to the end of the drill rod which extends from the taphole plug can be rapidly and automatically accomplished, a taphole may theoretically be opened within one minute after a decision to open the hole has been made. This is a very significant savings in time when compared to the prior art tapping operations wherein a plug was drilled from the taphole.
Unfortunately, the theoretically possible savings in time in opening a furnace taphole discussed above have not been realized because the engagement of a conventional percussive drill with a drill rod has proven to be a time consuming task. It is customary for a percussion-type taphole drill to be mounted on and movable along a support bar. This support bar must be provided with a guide and support device at the end thereof which approaches closest to the furnace wall in order to provide the necessary support for the drill rod before or after it is supported in the taphole. The end of the taphole drill support bar, when being moved from the inoperative or rest position into its working position in alignment with the taphole, performs what may generally be described as a double movement. The last stage of this movement is in the vertical direction, i.e., in a direction parallel to the wall of the furnace, while the initial phase of movement is either along a horizontal or inclined approach trajectory. Because of this final vertical phase of movement, however, a guide plate which defines a drill rod receiving channel at the end of the drill support bar cannot be caused to engage the end of the drill rod which extends outwardly from the taphole. Thus, it has previously been necessary to perform the time-consuming task of dismantling the support plate from the drill support bar, engaging the plate with the drill rod supported in the taphole plugging material, causing the drill to engage the rod and then reattaching the support plate to the drill support bar. In addition to being a time consuming task, this work must be performed adjacent the furnace wall where there is the ever present danger of injury.
It is to be observed that a recently introduced drill support mechanism, as depicted in aforementioned U.S. Pat. No. 4,201,373, eliminates the necessity of utilizing two different phases of motion to move a percussive drill from the inoperative to the operative position. Thus, the apparatus of U.S. Pat. No. 4,201,373 enables the movement of the end of the drill support bar along a continuous trajectory which includes an approach component and a final positioning component which is relatively small and comprises the descent of the drill into the operative position. This compound movement places the drill support bar practically in alignment with a continuation of the axis of the taphole, and thus also in alignment with the drill rod, as the guide plate at the end of the support bar approaches the end of the drill rod. Nevertheless, even when employing the drill support mechanism of U.S. Pat. No. 4,201,373, there is a problem in insuring that the exposed end of the drill rod will be guided into the rod receiving channel in the support plate at the end of the support bar.